effect of flip angle error for t1 bias correction in mri fat fraction estimation march 22, 2011...
TRANSCRIPT
![Page 1: Effect of Flip Angle Error for T1 Bias Correction in MRI Fat Fraction Estimation March 22, 2011 Issac Yang Supervisor: Charles McKenzie, PhD Department](https://reader035.vdocument.in/reader035/viewer/2022062722/56649f305503460f94c4a687/html5/thumbnails/1.jpg)
Effect of Flip Angle Error for T1 Bias Correction in MRI Fat Fraction
EstimationMarch 22, 2011
Issac YangSupervisor: Charles McKenzie, PhDDepartment of Medical Biophysics
University of Western Ontario
![Page 2: Effect of Flip Angle Error for T1 Bias Correction in MRI Fat Fraction Estimation March 22, 2011 Issac Yang Supervisor: Charles McKenzie, PhD Department](https://reader035.vdocument.in/reader035/viewer/2022062722/56649f305503460f94c4a687/html5/thumbnails/2.jpg)
Background and Motivation
• Non-Alcoholic Fatty Liver Disease (NAFLD) is becoming the most common chronic liver disease– Affects 30% of the Western
population
• Fat depositing in liver cells (steatosis)
• Associated with metabolic syndromes– Obesity, type II diabetes
Normal
Fatty Liver
![Page 3: Effect of Flip Angle Error for T1 Bias Correction in MRI Fat Fraction Estimation March 22, 2011 Issac Yang Supervisor: Charles McKenzie, PhD Department](https://reader035.vdocument.in/reader035/viewer/2022062722/56649f305503460f94c4a687/html5/thumbnails/3.jpg)
Background and Motivation
• NAFLD is asymptomatic• Current procedure of detection
is liver biopsy– Invasive procedure
• Complications involves minor bleeding, hospitalization, and (rarely) death
– Steatosis distribution is inhomogeneous• Prone to sampling error
• MRI offers a non-invasive alternative– Unaffected by sampling error
![Page 4: Effect of Flip Angle Error for T1 Bias Correction in MRI Fat Fraction Estimation March 22, 2011 Issac Yang Supervisor: Charles McKenzie, PhD Department](https://reader035.vdocument.in/reader035/viewer/2022062722/56649f305503460f94c4a687/html5/thumbnails/4.jpg)
Obtaining Fat Fractions
• An MRI technique called IDEAL was used– Allows production of
separate fat and water signal images.
Fat + Water
Water Fat
IDEAL
Fat Fraction = +
![Page 5: Effect of Flip Angle Error for T1 Bias Correction in MRI Fat Fraction Estimation March 22, 2011 Issac Yang Supervisor: Charles McKenzie, PhD Department](https://reader035.vdocument.in/reader035/viewer/2022062722/56649f305503460f94c4a687/html5/thumbnails/5.jpg)
Bias in Fat Fraction
• Signals in each pixel is characterized by the equation
• T1 values for fat is significantly different from T1 of water– Typically: T1f=382ms, T1w=809ms at 3.0 T in vivo
• Difference in T1 values cause unequal weighting of water and fat signals in fat fraction equation
![Page 6: Effect of Flip Angle Error for T1 Bias Correction in MRI Fat Fraction Estimation March 22, 2011 Issac Yang Supervisor: Charles McKenzie, PhD Department](https://reader035.vdocument.in/reader035/viewer/2022062722/56649f305503460f94c4a687/html5/thumbnails/6.jpg)
![Page 7: Effect of Flip Angle Error for T1 Bias Correction in MRI Fat Fraction Estimation March 22, 2011 Issac Yang Supervisor: Charles McKenzie, PhD Department](https://reader035.vdocument.in/reader035/viewer/2022062722/56649f305503460f94c4a687/html5/thumbnails/7.jpg)
Current Method
• T1 weighting in the signal increases with flip angle
• Current method of mitigating bias is to use a low flip angle.– Decreases signal intensity– Reduced Signal to Noise
Ratio (SNR)
![Page 8: Effect of Flip Angle Error for T1 Bias Correction in MRI Fat Fraction Estimation March 22, 2011 Issac Yang Supervisor: Charles McKenzie, PhD Department](https://reader035.vdocument.in/reader035/viewer/2022062722/56649f305503460f94c4a687/html5/thumbnails/8.jpg)
Bias Correction
• Bias can be reduced by performing corrections to the image by using estimated T1 values.
• This method assumes known and uniform flip angle— Untrue for fields of 3.0T and above due to RF pulse
inhomogeneity— Flip angle measurements should be performed to further
reduce error
![Page 9: Effect of Flip Angle Error for T1 Bias Correction in MRI Fat Fraction Estimation March 22, 2011 Issac Yang Supervisor: Charles McKenzie, PhD Department](https://reader035.vdocument.in/reader035/viewer/2022062722/56649f305503460f94c4a687/html5/thumbnails/9.jpg)
Method
Fat Image
Water Image
Flip Angle Map
Bias Correction
Corrected Fat Image
Corrected Water Image
Fat Fraction
Map
Bias Correction
T1w Estimate
T1f Estimate
![Page 10: Effect of Flip Angle Error for T1 Bias Correction in MRI Fat Fraction Estimation March 22, 2011 Issac Yang Supervisor: Charles McKenzie, PhD Department](https://reader035.vdocument.in/reader035/viewer/2022062722/56649f305503460f94c4a687/html5/thumbnails/10.jpg)
Results
• Flip angle measurements show true flip angle to be 9 degrees on average– Prescribed 12 degrees– 25% lower than expected
• T1 measurements yielded:– T1w=274ms, T1f=181ms– Estimated values: T1w=350ms, T1f=200ms
Flip Angle Map
![Page 11: Effect of Flip Angle Error for T1 Bias Correction in MRI Fat Fraction Estimation March 22, 2011 Issac Yang Supervisor: Charles McKenzie, PhD Department](https://reader035.vdocument.in/reader035/viewer/2022062722/56649f305503460f94c4a687/html5/thumbnails/11.jpg)
Correction Results
![Page 12: Effect of Flip Angle Error for T1 Bias Correction in MRI Fat Fraction Estimation March 22, 2011 Issac Yang Supervisor: Charles McKenzie, PhD Department](https://reader035.vdocument.in/reader035/viewer/2022062722/56649f305503460f94c4a687/html5/thumbnails/12.jpg)
Discussion
• Measured fat fractions was brought closer to the true fat fraction value for phantoms
![Page 13: Effect of Flip Angle Error for T1 Bias Correction in MRI Fat Fraction Estimation March 22, 2011 Issac Yang Supervisor: Charles McKenzie, PhD Department](https://reader035.vdocument.in/reader035/viewer/2022062722/56649f305503460f94c4a687/html5/thumbnails/13.jpg)
Conclusion
• Experiments suggest that including flip angle mapping into imaging protocol would decrease fat fraction bias
![Page 14: Effect of Flip Angle Error for T1 Bias Correction in MRI Fat Fraction Estimation March 22, 2011 Issac Yang Supervisor: Charles McKenzie, PhD Department](https://reader035.vdocument.in/reader035/viewer/2022062722/56649f305503460f94c4a687/html5/thumbnails/14.jpg)
Acknowledgement
McKenzie Lab
Dr. Charles McKenzieDr. Trevor WadeDr. Lanette Friesen-Waldner
Curtis WiensBryan AddemanYifan CuiSamantha Flood
Bartha Lab
Dr. Robert BarthaDr. John DrozdJacob Penner
![Page 15: Effect of Flip Angle Error for T1 Bias Correction in MRI Fat Fraction Estimation March 22, 2011 Issac Yang Supervisor: Charles McKenzie, PhD Department](https://reader035.vdocument.in/reader035/viewer/2022062722/56649f305503460f94c4a687/html5/thumbnails/15.jpg)
Thank You For Your Attention
Questions?